This invention relates in general to the construction of testing tubes and in particular to a new and useful filter element for such tubes.
Testing tubes are generally known. They are used in combination with manual or automatic pumps for the qualitative or quantitative analysis of gases, vapors or aerosols. Before the gas-tight test tubes are used, their tips are broken off, and a certain volume of the medium to be tested is sucked through. The testing tube contains certain reagents, which then form with the respective medium mostly colored reaction products. The applicant's assignee supplies about 200 different test tubes for the various media. A major part of the test tubes is equipped with a filter part to be traversed by the test medium.
A known testing tube for measuring arsenic trioxide aerosols in air contains in the glass tubes provided with break-off tips successively in the direction of flow, a reagent ampule filled with diluted sulfuric acid, a filter paper flush with the glass wall and impregnated with zinc powder, a granular collecting layer of silica gel, a granular separating layer of inert quartz, and a granular indicating layer of silica gel impregnated with gold chloride. The filter is held by an elastic holding element on the silica gel layer. Above the holding element is then the reagent ampule, which is held at its other end again by a holding element. A complete deposit of the aerosols on the filter paper, which is necessary for an exact evaluation, requires a tight seal on the inner wall of the glass tube. This is very difficult to achieve, due to the great manufacture-related tolerances of the glass tubes and of the other elements (German Pat. No. 2,926,711).